We make sound by pushing air from our lungs along our vocal cords (or vocal folds) that then vibrate to make sound. We have muscles that control the shape of the vocal folds, and thus make them vibrate in different ways. The mouth, tongue, and lips then further direct the air to alter the sound. Your voice is a combination of these three systems; the lungs pushing out air, muscles changing the shape of the vocal folds, and your mouth, tongue and lips changing shape.